The invention relates to an excavation support structure that is constructed using deep cement soil mixing (DSM) and shallow cement soil mixing (SSM) to provide, in effect, a self-supporting, composite gravity wall structure.
In general, as shown in FIG. 20, DSM and SSM are soil treatment techniques in which soil 900 is blended with cement and other materials introduced in dry or mixed form through a hollow, rotating mixing shaft 910 equipped with cutting heads 920. The shaft 910 is mounted vertically on a suitable carrier 930. The resulting cemented soil 940 material generally has a higher strength and lower compressibility than the native soil 900. DSM and SSM have been used in a number of applications, such as hydraulic cut-off walls, excavation support walls, ground treatment, liquefaction mitigation, in situ reinforcement, and environmental remediation. For example, in an excavation support application, an overlapping row or array of soil-cement columns 940 may be formed along the excavation line. The resulting wall of soil-cement columns provides structural support and ground water control for excavation projects.